1. Field of the Invention
The present invention relates generally to a compound semiconductor single crystal suitable for use as a substrate for epitaxial deposition of a light emitting device which emits green light, and more particularly to a GaP single crystal.
2. Description of the Prior Art
The demand for high luminance GaP green-light light-emitting diodes (LEDs) has increased year after year. However, since luminance reduction is caused by various reasons, a satisfactory solution to the foregoing demand has not been proposed. For example, when a liquid-phase epitaxial layer is deposited on a GaP single crystal substrate to fabricate an epitaxial wafer for a green light LED, a problem occurs in that the luminance at a particular portion of the substrate becomes inadequate.
Through an investigation on the impurity concentration of GaP single crystal substrates involving the inadequate luminance problem and of GaP single crystal substrate free from the inadequate luminance problem, the present inventors have found that a definite correlation exists between the luminance and the concentrations of particular impurities. Based on this finding, the present inventors have completed the present invention.